are they seperate FAS2240's or are they a single chassis with two controllers?
If they are two completely seperate chassis and controllers then no problem. If they are a two controllers in the same physical chassis then it wont be supported but would probably work. (possibly unpredictably) .
Upgrading from 8.1.1RC1 to 8.1.4P4 is supported as far as i remember, if you have access to myASUP then you can generate an upgrade plan from there based on your latest autosupport data. i think the jump up upgrades were from 8.0.x to 8.2.x ??
Theres no point upgrading the controller that you're planning on converting to cDoT. talk to your account team and they can get you eval licenses for cDoT you will need to zero the disks out and install the new OS. which is not that hard, but could be daunting if you've never done cDoT before.